As is known in the art, many applications involving semiconductor devices require mechanisms to dissipate heat. For example, fans can be used to force air flow for enhancing heat dissipation. Heat sinks can increase surface area to transfer heat away from devices. Known systems can also include liquid cooling by circulating a fluid to dissipate heat.
Micro-channel cold plates utilizing phase-change heat removal have emerged as a viable technique for coping with increased dissipation density in semiconductor devices. However, the increased pressure loss associated with micro-channels necessitates shortening of flow paths and forces flow path parallelism to achieve optimal thermal and hydraulic performance.
A variety of complex, active component flow-balancing devices for two-phase flows are commonly used in the HVAC&R (Heating, Ventilation, Air Conditioning & Refrigeration) industry. However, such mechanisms include relatively large, complicated mechanical elements (springs, diaphragms, etc.) that are not suitable for reliable integration as part of a monolithic cold plate.
Conventional implementations of parallel micro-channel phase-change cooling schemes for spatially varying thermal loads have design specific flow arrangements, which limit applicability and increase complexity. U.S. Pat. No. 7,218,519 to Prasher et al., which is incorporated herein by reference, discloses micro-channel cold plates having channels designed with a priori knowledge of high and low heat load locations. Thus, the cold plates disclosed by Prasher are limited to particular board layouts with integrated circuits, such as microprocessors, in given locations. FIGS. 1A and 1B show implementations from Prasher having channels for low and high heat areas defined by the locations of microprocessors. Thus, Prasher discloses a cold plate that is limited to one particular board layout.
As is further known in the art, coolant flow misdistribution in phase change cooling systems with varying heat loads on parallel flow paths is the result of uneven vapor fraction at the flow path exit. When one flow path dissipates more heat than another path, the total volumetric flow of vapor in that path is greater on average, thereby incurring a larger pressure drop. Since parallel paths must have equivalent pressure drops, the flow rates for the flow paths dissipating less heat increase, while the flow rates for paths dissipating more heat decrease, until an equivalent pressure drop across all paths is established to restore equilibrium. The consequence is that the flow paths with larger heat loads can be starved of fluid flow, degrading thermal performance. Relatively small amounts of vapor can significantly impact pressure drops. The phenomenon of pressure drop multiplication due to vapor fraction is illustrated in FIG. 2, from Kojasoy, G. et al., “Two-Phase Pressure Drop in Multiple Thick and Thin Orifice Plates,” Experimental and Fluid Science, 1997, 15:347-358.